1. Field of the Invention
The present invention relates to a curve approach control apparatus which enables a car to negotiate a curved road at an appropriate speed.
2. Description of the Related Art
Many curve approach control apparatus have been proposed which use road map data in a navigation device to detect an overspeed state of a car with respect to a curve in front and activate an alarm or deceleration control. For example, Japanese Patent Unexamined Publication No. Hei. 4-236699 (JP-A-4-236699) discloses a technology which determines an appropriate approach speed at which to enter the curve based on a radius of curvature of a curve in a travel path (guided path) set in the navigation device according to an input from a driver and on detected road surface conditions and, when an actual car speed is higher than the calculated value of the appropriate approach speed, issues an alarm to alert the driver to the need for reducing the car speed, or automatically activates a car speed reduction means in combination with the alarm.
The navigation device, when the guided path is not set, estimates a path that the car will travel according to a road kind and a road width and outputs node data on the estimated path to the curve approach control apparatus.
Where a path that turns left or right at an intersection is set as a guided path or estimated path (generally referred to as a set path) in the navigation device, the driver may travel in a direction different from the set path. In such a case, the technology of JP-A-4-236699 described above continues the alarm or deceleration control for a while as the car moves through the intersection. This control makes the driver feel incongruous.
The present invention has been accomplished under this circumstance and provides a curve approach control apparatus which prevents unnecessary alarm or deceleration while passing through an intersection and thereby avoids giving a sense of incongruity to the driver.
To solve the above problem, in a curve approach control apparatus according to the first aspect of the present invention, which uses road information from a navigation device to perform an alarm control or a deceleration control on a curve in front, when it is decided that a driver is going to travel straight through the curve, the alarm control or the deceleration control is inhibited.
In a second aspect according to the present invention, when a straight travel state of a car is detected, it is decided that the driver is going to travel straight.
In a third aspect according to the present invention, the straight travel state is judged by comparing an actual measured value of a turning motion parameter of a car and an estimated value of a turning motion estimated from a car speed and a curve""s radius of curvature.
In a fourth aspect according to the present invention, the turning motion parameter is a yaw rate.
In a fifth aspect according to the present invention, the turning motion parameter is a lateral acceleration.
In a sixth aspect according to the present invention, the turning motion parameter is a steering wheel angle.
In a seventh aspect according to the invention, when the car is in an accelerating state, it is decided that the driver is going to travel straight.